Connection Time Out when Downloading Forms

Dear ODKers,
I am facing a problem when trying to download forms in my Aggregate
server v1.04. From within the institutions network (work) my Aggregate
server is on 192.168.x.y. I can set ODK collect to download forms and
submit forms, no problem. However from outside the institution, I
asked the IT department to give the aggregate server a public IP so it
is accessible from outside. So now I have a public IP
which when I navigate from my samsung galaxy I get the lovely Apache
Tomcat welcome screen, however when I navigate to
ODKAggregate, the Galaxy tab automatically reconfigures the IP to the
original 192.168.x.y/ODKAggregate (which of course is only accessible
from within the institutes network, not outside). Even when I go to
ODK Collect-> Preferences->Server and set this to,
then I go to download foms, I can access and see forms on the server,
however when I try download the form ODKCollect tells me (after a bit
of a wait) "Download Result: Elephant Death Form - Connect to /
192.168.x.y:80 timed out" - it seems even Collect is resolving to the
internal IP rather than the public IP I set in Collects' preferences.
Does anyone know why that is and what I can do to remedy that?

Thanks in advance,